1. Field of the Invention
The invention relates to a medical guide wire to facilitate inserting a catheter into a cardiovascular system and hepatovascular system, and particularly concerns a medical guide wire with an improved leading distal end structure.
2. Description of Related Art
A medical guide wire has been used to assist a very thin and flexible catheter to insert it into a blood vessel, to check its diseased area with an angiography to facilitate using a balloon catheter to treat a coronary stenosis, and to insert the catheter into a hepatovascular system to cure a diseased area of the liver.
In these applications, the leading distal end of the medical guide wire is introduced into the diseased area through a sinuous vascular system, a bifurcated blood vessel or a vascular stenosis by a “push-pull and turn” manipulation at a hand access portion located outside a subject patient.
To achieve a smooth manipulation when inserting the leading distal end into the diseased area, the medical guide wire must have multi-mechanical properties. The multi-mechanical properties include high flexibility, good torque transmissibility and high bending characteristics with a small radius of curvature together with a good steerability by the hand access portion.
By way of illustration, FIG. 12 shows a diseased area (P) in which a completely obstructed area 25 occurs in a blood vessel (T) consisting of the intima 21, the media 22 and the adventitia. The completely obstructed area 25 is 10-15 mm long and filled with occlusive substances such as atheroma, plaque, thrombi. Both ends of the obstructed area 25 are calcified with a deposit of calcium salt to form a hardened fibrous cap.
In this example, a user steers a leading distal end 106 of a guide wire (G) at the obstructed area 25 to feel for a reaction against a concave area of the vascular wall based on a sensation coming to the hand access portion. Then, the user moves the guide wire (G) to a normal position (GA) by repeatedly pushing and turning the leading distal end 106 within a range of 2-3 mm. In order to efficiently and precisely perform the manipulation, it is necessary to give the guide wire (G) a high flexibility, a good torque transmissibility and sensitivity against the vascular wall. When the leading distal end 106 of the guide wire (G) lacks the flexibility, the leading distal end 106 does not follow a curved profile at the sinuous blood vessel. The leading distal end 106 is prone to remaining straight and likely advances into the intima 21 and the media 22 so as to often result in a vascular perforation as shown in FIG. 13. Otherwise, the leading distal end 106 unfavorably induces a false lumen 26 as shown in FIG. 14. In order to avoid these problems, it is necessary for the leading distal end 106 to have a bending characteristics that allow it to bend at an extremely small radius of curvature.
A medical guide wire with some of these mechanical properties has been introduced in a Laid-open Japanese Patent Application No. 4-292175. In this prior art reference, a flexible and elongated shaft portion 100 is disclosed as a main portion with its rear portion manipulated by a hand access portion 107 as shown in FIG. 15. A front distal end portion of the shaft portion 100 has a thin core wire 102 which is inserted into a helical coil body. A head plug 104 is secured to both top distal front end of the core wire 102 and the helical coil body 103 so as to form the leading distal end 106. As shown in FIGS. 16 and 17, the leading distal end 106 has a core line securement portion 111 somewhat remote (e.g., approximately 26 mm) from the front distal end of the head plug 104 to secure the helical coil body 103 to the core wire 102 by means of a soldering procedure. A lengthwise extension of the core wire 102 from the core line securement portion 111 to a proximal end of the head plug 104, progressively increases its breadth (m) variably toward the front distal end of the head plug 104 while successively reducing its thickness (h) variably to taper off toward the front distal end of the head plug 104 so as to form a duckbill structure 130.
The leading distal end 106 of the duckbill structure 130 has as its objective merely to allow a selective insertability against the bifurcated portion of the blood vessel, and accordingly, diminishing detection of the stenosis and the obstructed area of the blood vessel, thus reducing an ablative ability against a narrow portion of the blood vessel and lowering the sensitivity against the vascular wall and the diseased area.
Therefore, it is an objective of the invention to overcome the above drawbacks by improving the indispensable mechanical properties so as to provide a high quality medical guide wire with good performance.